Validation of In Vivo Patellar Tracking with a Custom-Made Clamp: A Fluoroscopy Study

Evaluation of patellar tracking has been suggested as an increasingly relevant diagnostic tool in patients with patellofemoral disorders. This study aimed to assess the accuracy of measuring in vivo patellar tracking with the use of a custom-made clamp. Nine healthy female college students participated. Sagittal-view fluoroscopy was used to track the movement of the clamp and the underlying patella of each subject's dominant leg during a lunge. The movement patterns (tilt angle and displacement) as well as the absolute angle/distance between the patella and clamp were investigated at 7 knee flexion angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°). The patella and clamp showed similar movement patterns (tilt angle: r= 0.94, P= 0.002; displacement: r= 0.90, P= 0.007). The root mean squared error of less than 3.5° and 0.6 cm were identified below knee flexion 60°. The absolute angle significantly changed at knee flexion 90° compared to 0° (P= 0.016). The absolute distance between the upper edge of the patella and clamp significantly changed at knee flexion 60° to 90° as compared to 0° (all P< 0.05). The angle/distance change may represent an influence of a skin motion artifact manifesting beyond knee flexion 60°. With careful consideration, the custom-made clamp may offer reasonably accurate representations of patellar motion that can be used to further study patella pathologies and develop computational models.